“The face coverings do not have to be hospital grade but need to cover the nose and mouth. For example, bandanas, fabric masks and neck gaiters are acceptable. Fabric covers and bandanas can be washed and used again,” health officials from San Francisco, San Mateo and Alameda counties said in similar statements. “Health officials do not recommend that the public use medical masks (N-95 or surgical masks), which are in limited supply and must be preserved for our health care workers and first responders.”

California officials said face coverings can prevent people from becoming infected with the new coronavirus or spreading it to others, but they stressed it should not be a substitute for physical distancing, hand washing and other measures.

“Face coverings could provide some additional protection against COVID-19, but Californians should not have a false sense of security if they choose to wear them. Make sure you’re also staying 6 feet away from other people if you have to leave your home to get groceries or prescriptions,” Dr. Mark Ghaly, secretary of the California Health and Human Services Agency, said in a statement.

State officials have said people should not use medical and surgical masks, which are desperately needed by medical personnel.

The federal Centers for Disease Control and Prevention has said healthy people do not need a mask if they are not working in healthcare or caring for an infected person. But in recent days, the CDC has been weighing whether to modify its recommendations and endorse the use of homemade masks.

At a Wednesday afternoon news briefing, Los Angeles Mayor Eric Garcetti said everyone performing essential tasks such as shopping for food should wear homemade, nonmedical face coverings, or even bandannas, as people in other countries have done.

Officials stressed that physical distancing rules remain in place.

“In addition to shelter-in-place and social distancing requirements, wearing a mask in public is an important tool to stop the community spread of this disease,” Dr. Scott Morrow, San Mateo County’s health officer, said in a statement. “People with no or mild symptoms may have coronavirus and not know it. Wearing face coverings helps protect others from exposure.”